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This page first made public: Nov 22, 2010

Lab 7: Future of the Cryosphere

The lab activity described here was developed by Erin Bardar of TERC for the EarthLabs project.

Use the button at the right to navigate to the student activity pages for this lab. To open the student pages in a new tab or window, right-click (control-click on a Mac) the "Open the Student Activity" button and choose "Open Link in New Window" or "Open Link in New Tab."

Investigation Summary and Learning Objectives

Warming temperatures are responsible for significant declines in sea ice thickness and extent in recent years. The loss of sea ice habitat due to melting ice is the primary threat to Polar bears. What will the future hold for the cryosphere and for the polar bears? Photo taken by Martha de Jong-Lantink. Image Source: Flickr.

In this culminating activity, students contemplate what the future might hold for climate and the cryosphere. In the first part of the lab, students consider potential changes in sea level that might be brought about by climate change and melting ice. In Part B, students use the online interactive "Earth Swings" to explore different aspects of sea change that emphasize the idea that Earth's surface is not static, but in fact has always been changing and will continue to change.

After completing this investigation, students will be able to:

explain what climate models predict for the future of the cryosphere

describe potential impacts on life as a result of predicted future changes to the cryosphere; and

explain how the cryosphere is an important indicator of global climate change.

For more information about the topic, read the section titled Background Information under Additional Resources below.

Activity Overview and Teaching Materials

In Part A: Students predict how massive melting of sea ice and land ice will each contribute to global sea level rise. They then design and construct a model to demonstrate both processes. Provide each small group of students with the following materials:

large bowl

water

ice cubes

rock or block of wood

ruler

additional craft supplies

Students are encouraged to come up with their own way to show how melting sea and land ice will contribute to sea level rise. They should find that sea ice does not contribute significantly to sea level rise because sea ice floating in ocean water displaces approximately the same amount of water as it contributes to the ocean when it melts.

To model sea ice, float a few ice cubes in a glass, bowl, or small aquarium tank of water. Mark the water level on the side of the container or add enough water so that the water level is even with the top edge. Place the container in direct sunlight or under a lamp so that ice cubes will melt relatively quickly. Monitor/measure any changes to the water level as the ice disappears.

If you use freshwater, the ice in the glass will not cause the water level to rise when it melts. When frozen and floating, ice displaces enough water to support its mass. When the ice melts, the added volume of water is the same as the volume that was displaced by the floating ice. In the oceans, sea ice expels salt when it freezes, so the ice itself is essentially freshwater ice. However, it is floating in salty water, which is denser than freshwater. Because the freshwater ice is less dense, it floats higher and displaces less water than it would if it were floating in freshwater. Therefore, when the ice melts, it contributes a slightly greater volume of melt water than it displaced when it was frozen. This means that melting sea ice can have a small, but real contribution to sea level rise.

Land Ice
The land ice model must begin with the ice being completely out of the water. For example, you could place a rock or wooden block in the bottom of a bowl or small tank to represent a land mass. Pour some water into the container so that the water level is slightly below the top of the "land". Mark the water level on the side of the container. Place a few ice cubes on top of the "land" and put the container in direct sunlight or under a lamp to melt the ice. Monitor/measure any changes to the water level as the ice disappears.

Glaciers or ice sheets, which are not in the oceans, will add volume to the oceans and increase sea level when they melt. Some degree of melting can also cause land ice to break off and slide into the ocean, which can contribute to sea level rise as the added ice displaces ocean water. Therefore, melting land ice has a much more significant impact on sea level rise than does melting sea ice.

Watch this video to see a simulation of how the melting of ice shelves and ice sheets affects sea level.

After completing their models, students interpret sea level rise data and use the online interactive Mountain of Ice: If the Ice Melts and a world map showing areas at or near sea level to see where sea level rise due to melting ice poses the largest threats.

In Part B: Students use the online interactive "Earth Swings" to explore different aspects of sea change that emphasize the idea that Earth's surface is not static, but in fact has always been changing and will continue to change. Concepts such as the coming and going of ice sheets, the motion of tectonic plates, the deformation of the Earth's crust due to glacier weight and ocean circulation and pH are presented as examples of changes to Earth's surface.

This visualization is still being developed. When it is is completed, students will be able to compare the rate of change of historical climate changes with the rate of change of anthropogenic changes, and read word analogies and see visuals to help them grasp the difference between slow natural changes and rapid, human induced changes. This rate of change comparison is presented through both a word analogy, and a visual timeline, to accommodate different learning styles. Two types of historical change will be featured: slow Earth swings (such as the last glacial maximum) and abrupt swings (such as the 8.2 Event and the Younger Dryas). The rate of change of these events can then be compared with each other, and with future projections.

Rough prototype: All six round buttons on the left are working. None of the sliders are working. Only in the "Ice or water" section is the "Climate Extremes" button working. The "Start over" button works throughout the interactive.

Printable Materials

To download one of the PDF or Word files below, right-click (control-click on a Mac) the link and choose "Save File As" or "Save Link As."

Additional Resources

Background Information

"Ice becomes liquid water when warmed to its melting point. Conversely, liquid water changes state to become ice when cooled to its freezing point. Earth's polar regions consist largely of ice, and exhibit dramatic changes in ice coverage in response to seasonal changes in temperature. An increase in temperature resulting from global warming could drastically affect the extent of polar ice. Whether those changes would cause sea level to rise depends on whether the ice is continental ice or floating ice.

Continental ice (such as glaciers and ice sheets) raises sea level as it melts. This happens because when ice on land melts, it adds water into the ocean that was not there before. This extra water raises sea level. For example, if the West Antarctic ice sheet melted, sea level would rise by at least 5 meters. That is a significant amount; even a rise of just one meter would displace roughly 100 million people along coastlines.

Floating ice (such as ice shelves, icebergs, and sea ice) would not have much effect on sea level. According to a physical concept known as Archimedes' principle, a floating object displaces an amount of water equal to its weight. In other words, floating ice displaces a volume of water approximately equal to the volume of water it would contribute as it melts; therefore, when floating ice melts, there is very little change in sea level.

However, although the melting of floating ice doesn't significantly affect sea level, there are other consequences. Variations in salinity and temperature drive global ocean circulation because of density differences; fresh water is less dense than salt water and warm water is less dense than cold water. This thermohaline circulation is sometimes referred to as the great ocean "conveyor belt" because it is one of Earth's main mechanisms for transporting energy. The formation of sea ice, which is primarily made of pure water, leaves behind salt in the water beneath the ice, resulting in saltier and colder water that sinks through the water below it, thereby promoting circulation. When ice melts, it adds fresh water to the ocean, decreasing salinity and affecting the circulation pattern. Any change to ocean circulation could have damaging effects on the water cycle and weather patterns.

In addition, a change in the temperature or salinity of ocean water disrupts habitats and could have harmful effects on marine life forms that are sensitive to such changes. The loss of sea ice in polar regions also threatens the survival of certain species, such as the polar bear, which depend on the ice for hunting and breeding. Furthermore, ice shelves act as buttresses, keeping glacial ice from reaching the ocean. Even if melting ice shelves would not increase sea level directly, the barrier that prevents ice sheets from sliding into the water would be gone, and the melting ice sheets would increase sea level."

Fact Sheet: Sea Level and Climate: "Global sea level and the Earth's climate are closely linked. The Earth's climate has warmed about 1°C (1.8°F) during the last 100 years. As the climate has warmed following the end of a recent cold period known as the "Little Ice Age" in the 19th century, sea level has been rising about 1 to 2 millimeters per year due to the reduction in volume of ice caps, ice fields, and mountain glaciers in addition to the thermal expansion of ocean water. If present trends continue, including an increase in global temperatures caused by increased greenhouse-gas emissions, many of the world's mountain glaciers will disappear. For example, at the current rate of melting, most glaciers will be gone from Glacier National Park, Montana, by the middle of the next century (fig. 1). In Iceland, about 11 percent of the island is covered by glaciers (mostly ice caps). If warming continues, Iceland's glaciers will decrease by 40 percent by 2100 and virtually disappear by 2200.

Most of the current global land ice mass is located in the Antarctic and Greenland ice sheets (table 1). Complete melting of these ice sheets could lead to a sea-level rise of about 80 meters, whereas melting of all other glaciers could lead to a sea-level rise of only one-half meter."